Washington: Geologists have discovered what they say is an ancient, lost landscape that lies deep beneath the sediment of the North Atlantic Ocean near the northern coast of Scotland.

The massive landscape with furrows cut by rivers and peaks that once belonged to mountains is believed to be some 56-million-year-old.

"It looks for all the world like a map of a bit of a country onshore. It is like an ancient fossil landscape preserved two kilometres beneath the seabed," senior study researcher Nicky White was quoted as saying by LiveScience.

The researchers, who used an advanced echo-sounding technique to find the landscape, said their data have so far revealed a landscape about 10,000 square km west of the Orkney-Shetland Islands that stretched above sea level by almost as much as 1km.

They suspect it is part of a larger region that merged with what is now Scotland and may have extended toward Norway in a hot, prehuman world.

The researchers, who detailed their findings in the journal Nature Geoscience, used high pressured air via metal cylinders, producing sound waves that travel to the ocean floor and beneath it, through layers of sediment.

Every time the sound waves encountered a change in the material, an echo bounced back and microphones trailing behind the ship on cables record these echoes.

From the information, they constructed 3-D images of the sedimentary rock below, said White, a geologist at the University of Cambridge in Britain.

The team found a wrinkly layer 1.2 miles (2km) beneath the seafloor -- evidence of the buried landscape, reminiscent of the mythical, lost Greek island Atlantis.

They traced eight major rivers, and core samples, taken from the rock beneath the ocean floor, revealed pollen and coal, evidence of land-dwelling life. But above and below these deposits, they also found evidence of a marine environment, including tiny fossils, indicating the land rose above the sea and then subsided — "like a terrestrial sandwich with marine bread," White said.

Now, the burning question, according to White, is what made this landscape rise up, then subside within 2.5 million years? "From a geological perspective, that is a very short period of time," he said.

He and colleagues have a theory pointing to an upwelling of material through the Earth's mantle beneath the North Atlantic Ocean called the Icelandic Plume. (The plume is centred under Iceland.)

The plume works like a pipe carrying hot magma from deep within the Earth to right below the surface, where it spreads out like a giant mushroom, according to White. Sometimes the material is unusually hot, and it spreads out in a giant hot ripple.

The researchers believe that such a giant hot ripple pushed the lost landscape above the North Atlantic, then as the ripple passed, the land fell back beneath the ocean.